The present invention relates to drill rigs, and more specifically to a mechanism for retaining drill bits on a blasthole drill rig.
Blasthole drill rigs are commonly used in the mining industry to drill through hard rock. Blasthole drill rigs can be found, for example, in coal, copper, and diamond mines throughout the world. A blasthole drill rig typically includes a base, a drill tower extending vertically from the base, and a drill pipe or pipes that are coupled to and supported by the drill tower, and extend into a borehole. Some blasthole drill rigs include a mechanism, such as a carousel, for holding drill bits. Changing the drill bits of blasthole drill rigs has traditionally been performed by an operator and requires manual alignment of the threads of the drill bit with the threads of the pipe string to which it will be mated.
One of the major difficulties in changing drill bits is ensuring that the threads on the drill bit are concentric to the threads in the drill pipe, since tight tolerances are required between the drill pipe and the drill bit when attaching or removing a drill bit from the drill string. Current bit carousels include pots that receive and hold the drill bits not in use. The pots are somewhat oversized to allow the drill bit to easily be inserted. However, the large size of the pots makes it difficult for drill bit changing systems to properly align the drill string and the drill bit. Due to the long length of the drill strings, any misalignment or tilt between the drill bit and the drill string is magnified. Also, some drill rigs include a mast that is stored horizontally, and is then adjustable to an upright vertical position, or to positions between a horizontal and upright vertical position. The drill carousel is coupled to the mast, such that the drill carousel also moves with the mast. A mechanism is therefore desired to hold the drill bits in place in the carousel and prevent the drill bits from falling out of the carousel when the mast is not in the upright, vertical position.
One attempt at solving this problem has been to use three cylinders to extend a drill bit lock through the carousel pot to hold the bit in place (an example is set forth in U.S. Pat. No. 8,342,236). This design is expensive, requiring three sets of hydraulic cylinders, pins, locks, and an accompanying routing. Furthermore, it is unlikely that a multiple cylinder design will hold the bit consistently centered in the pot. For example, if the three cylinders are fed from the same hydraulic line, as one lock engages the drill bit the pressure in the cylinder will increase, forcing flow of hydraulic fluid to the other cylinders. In this instance, the lock will hold the drill bit in the position in which it was placed in the pot, rather than moving the bit to the center of the pot.